Pathophysiology and treatment of bone edema: focus on the knee

Abstract

Bone edema is a frequent condition that can involve several joints, especially the hip and knee. The radiological signal patterns for knee bone marrow edema are typically nonspecific. In recent literature, the general term “bone edema” has been replaced with the expressions “bone edema syndrome” or “bone edema lesions”. The causes of this condition can be traumatic, metabolic, inflammatory or micro-vascular, and may determine blood stasis, increased intra-bone pressure and, consequently, bone ischemia. The outcome of bone edema syndrome is variable, ranging from complete healing to osteonecrosis (ON), depending on the repair response. Pain is the main symptom; the most important differential diagnoses in bone edema syndrome are traumatic injuries, bone tumors or neurosensory changes. At the level of the knee, lesions can be distinguished into traumatic versus atraumatic, reversible versus irreversible, and subchondral versus joint-extended. Traumatic cases are the consequence of impact with bony surfaces impact and the most frequent mechanisms are pivot-shift, hyper-extension or varus-valgus stress; patellar luxation may contribute too. In contrast, atraumatic lesions are divided into reversible (regional migratory osteoporosis or algo-dystrophic syndrome) or irreversible such as avascular necrosis or spontaneous osteonecrosis of the knee (SONK). In recent literature, a spontaneous trabecular bone insufficiency fracture pattern (spontaneous insufficiency fracture of the knee, SIFK) has also been identified. This can self-limit and resolve spontaneously or degenerate into more severe forms of necrosis. Conservative treatment is considered in small lesions (< 3.5 cm2) or early cases of SONK and SIFK. It consists of partial load bearing, physical therapy, painkillers and treatment with bisphosphonate/prostacyclin. Surgical treatment, on the other hand, is reserved for patients with persistent pain after conservative treatment, meniscal extrusions or clear signs of marked ON. We here aim to provide a review of the current literature on bone edema injuries of the knee, focusing on the different clinical features and most recent effective treatments. KEY WORDS: Bone marrow edema, Knee, SONK, SIFK, AVN.